Position sensing is used to gain information about an event or a continuously varying condition. Position sensors known in the industry include resistive contacting networks, inductively coupled ratio sensors, variable reluctance devices, capacitively coupled ratio detectors, optical detectors using the Faraday effect, photo-activated ratio detectors, and electrostatic ratio detectors.
There are a variety of known techniques for angular position sensing. Each of these technologies offers a unique set of advantages and limitations. Of these technologies, magnetic sensing is known to have a unique combination of long component life and excellent contamination resistance. In magnetic sensing, a magnetic field dependent on the angular position is sensed and used to measure the angular position.
In the automotive industry, position sensors are widely used to measure crankshaft position in such applications as engine ignition timing. Examples of patents pertinent to the present invention include:
U.S. Pat. No. 5,712,561 to McCurley et al. for a field position sensor with improved bearing tolerance in a reduced space; PA1 U.S. Pat. No. 3,112,464 to Ratajski et al. for a Hall effect translating device; PA1 U.S. Pat. No. 4,142,153 to Smith for a tachometer measuring speed and direction of shaft rotation with a single sensing element; PA1 U.S. Pat. No. 4,293,837 to Jaffe et al. for a Hall effect potentiometer; PA1 U.S. Pat. No. 4,570,118 to Tomczak et al. for an angular position transducer including permanent magnets and Hall effect device; PA1 U.S. Pat. No. 4,726,338 to Decker for a device for controlling internal combustion engines; PA1 U.S. Pat. No. 4,744,343 to Bisenius for a device for controlling an internal combustion engines; PA1 U.S. Pat. No. 4,848,298 to Schleupen for a device for controlling internal combustion engine; PA1 U.S. Pat. No. 4,942,394 to Gasiunas for a Hall effect encoder apparatus; PA1 U.S. Pat. No. 5,055,781 to Sakakibara et al. for a rotational angle detecting sensor having a plurality of magnetoresistive elements located in a uniform magnetic field; PA1 U.S. Pat. No. 5,115,239 to Ushiyama for a magnetic absolute position encoder with an undulating track; PA1 U.S. Pat. No. 5,159,268 to Wu for a rotational position sensor with a Hall effect device and shaped magnet; PA1 U.S. Pat. No. 5,258,735 to Allwine for a multi-pole composite magnet used in a magnetic encoder; and PA1 U.S. Pat. No. 5,313,159 to Allwine for a magnetic encoder with composite magnet.
One problem with current electronic ignition systems is that they use variable reluctance (VR) sensors for measuring crank position. Such sensors magnetically detect variable reluctance patterns symmetrically spaced on a magnetic steel gear circumference. The symmetrical spacing is typically arranged in a 36 symmetrical, geartooth pattern or 10.degree. resolution spacing, which by design provides relative mechanical crankshaft position. However, VR crank sensors are not very reliable when they are used to detect ignition misfire events. The lack of reliability is due to poor signal quality, resolution, and external influences (noise) affecting the sensor signal and thereby inducing false misfire events.
In an effort to override the deficiencies of VR crank sensors in detecting ignition misfire events, filtering or masking schemes have been introduced in the misfire algorithm to attempt to determine between a true and a false misfire event. If these algorithms are incorrectly designed or produced, they may fail to meet the stringent California Air Resource Board emission standards. This failure scenario is potentially a large warranty cost burden to both the consumer and the manufacturer.
The obvious advantage for using VR sensors for the ignition and misfire systems is low cost and high sensor durability. Yet, the limitations of using VR sensors is low voltage output at low cranking speeds, which are generally undetectable by the electronic control module at crank speeds under 30 RPM. Other disadvantages of VR sensors for precision, position measurement applications are poor output signal integrity, accuracy, repeatability, and low resolution.
Thus, there is a need for a magnetic sensor, which can identify cylinder position at or below 15-20 RPM. Such a sensor would improve emission control at engine ignition start, and can also improve the crankshaft position identification response times. Further, there is a need to provide a magnetic sensor that will be conducive to extreme automobile environments and that is adaptable to present electronic control modules. These, and other identified needs, are satisfied by the present invention.